The
Antarctic ice sheet stores 90 percent of Earths frozen freshwater. Its
freezing and melting dynamics have many implications for climate change. Now,
scientists Eric Rignot from NASAs Jet Propulsion Laboratory and Stanley
Jacobs from Columbia Universitys Lamont-Doherty Earth Observatory reveal
in the June 14 issue of Science that the bottoms of Antarctic ice shelves are
melting more rapidly at their grounding lines  where ice detaches from
the seafloor and begins to float  than previously thought.

Its important because in the climate machine, which includes interactions
among ice, atmosphere and oceans, the component that has been overlooked is
ocean-ice interaction, says Terence Hughes, glaciologist at the Institute
of Quaternary and Climate Studies at the University of Maine. Using satellite
data, a means that has revolutionized the science, the authors better constrain
an important and extremely vulnerable part of the climate system, the ice sheets.

Satellite radar interferometry, a technique that measures the change in size,
velocity and shape of an object, helped precisely locate the grounding lines
of 23 ice shelves extending from ice sheets.

Depths at which ice shelves detach from the seafloor vary. The ocean water is
2 to 3 degrees above freezing and, due to its saline composition, is able to
melt the ice. At depth, increasing pressure causes greater melting.

Although the authors suggest that melt rates maintain the equilibrium of the
Antarctic ice sheet, they estimate that a 0.1 degree Celsius increase in ocean
temperatures will lead to melt increases of a meter per year. A change
of 0.1 degree Celsius is not unrealistic, and a meter per year thinning of ice
is a large rate. In a hundred years an ice shelf can disappear, Rignot
says.

Hughes agrees. This research does change the way we consider the Antarctic
ice sheet. We are getting at the underlying mechanism that causes ice sheets
to melt and we see that this melting is happening very quickly.
Salma Monani